Control of reaction zone severity by response to octane number of effluent liquid at reaction pressure

ABSTRACT

An improved control system for adjusting and controlling reaction zone severity in a continuous flow hydrocarbon conversion process, wherein a hydrocarbon charge stock is passed through a reaction zone at conversion conditions comprising elevated temperature and pressure, and the resulting product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon constituents. A sample of liquid phase effluent is continuously passed without intervening depressurization into a hydrocarbon analyzer which adjusts the reaction severity, and preferably heat input to the reaction zone, in response to the octane number of the liquid phase of the effluent. The octane measurement is effected by an analyzer comprising a stabilized cool flame generator with a servo-positioned flame front which provides a real time output signal indicative of sample octane number.

United States Patent Bajek et al.

ll :Nap/H/m Charge Slack Inventors: Walter A. Bajek, Lombard; James".McLaughlin, La Grange, both of III.

Universal Oil Products Company, Des Plaines, Ill.

The portion of the term of this patent subsequent to Mar. l4, I989, hasbeen disclaimed.

Filed: Sept.'3, 1971 Appl. No.: 177,801

Related US. Application Data Con tinuation'in-part of Ser. No. 868,460,Oct. 22, I969, abandoned.

Assignee:

Notice:

US. Cl 23/253 A, 23/253 PC, 23/263,

23/288 R, 208/139 208/DIG. 1 Int. C|..... B01] 9/04, Clog 35/04, G011]33/00 Field of Search 23/253 A, 253 PC, 23/230 A, 230 PC; 208/l39, DIG.1, I38, 163

References Cited UNITED STATES PATENTS 3/l972 Bajek et al 23/253 A.*Aug. 7, 1973 Primary Examiner- Joseph Scovronek Attorney-James R.Hoatson, Jr. et al.

[57] ABSTRACT An improved control system for adjusting and controllingreaction zone severity in a continuous flow hydrocarbon conversionprocess, wherein a hydrocarbon charge stock is passed through a reactionzone at conversion conditions comprising elevated temperature andpressure, and the resulting product effluent is separated into a vaporphase and into a liquid phase comprising gasoline boiling rangehydrocarbon constituents. A sample of liquid phase effluent iscontinuously passed without intervening depressurization into ahydrocarbon analyzer which adjusts the reaction severity, and preferablyheat input to the reaction zone, in response to the octane number of theliquid phase of the effluent. The octane measurement is effected by ananalyzer comprising a stabilized cool flame generator with aservo-positioned flame front which provides a real time output signalindicative of sample octane number.

14 Claims, 3 Drawing Figures Ne! Gas 1' Preh eater Separator Nat LIqU/d7'0 Fracr/onarian Octane Man/tar FIELD OF THE INVENTION This applicationis a continuation-in-part ofour copending application Ser. No. 868,460,filed Oct. 22, I969 and now abandoned.

The invention of this application is a process control application ofthe hydrocarbon analyzer described in U.S. Pat. No. 3,463,613 issuedAug. 26, 1969 to E.R. Fenske and J .l-l. McLaughlin, all the teachingsof which, both general and specific, are incorporated by referenceherein.

As set forth in U.S. Pat. 3,463,613, the composition ofa hydrocarbonsample can be determined by burning the sample in a combustion tubeunder conditions to generate therein a stabilized cool flame. Theposition of the flame front is automatically detected and used todevelop a control signal which, in turn, is used to vary a combustionparameter, such as combustion pressure, induction zone temperature orair flow, in a manner to immobilize the flame-front regardless ofchanges in composition of the sample. The changein such combustionparameter required to immobilize the flame following a change of samplecomposition is correlatable with such composition change, An appropriateread-out device connecting therewith may be calibrated in terms of thedesired identifying characteristic of the hydrocarbon sample, as, forexample, octane number.

Such an instrument is conveniently identified as a hydrocarbon analyzercomprising a stabilized cool flame generator with a servo-positionedflame front. The type of analysis effected thereby is not acompound-bycompound analysis of the type'presented by instruments suchas mass spectrometers or vapor phase chromatographs. On the contrary,the analysis is represented by a continuous output signal which isresponsive to and indicative of hydrocarbon composition and, morespecifically, is empirically correlatable with one or more conventionalidentifications or specifications of petroleum products such as Reidvapor pressure, ASTM or Engler distillations or, for motor fuels, knockcharacteristics such as research octane number, motor octane number orcomposite of such octane numbers.

For the purpose of the present application, the hydrocarbon analyzer isfurther limited to that specific embodiment which is designed to receivea hydrocarbon sample mixture containing predominantly gasoline boilingrange components, and the output signal of which analyzer provides adirect measure of octane number, i.e., research octane, motor octane ora predetermined composite of the two octane ratings. For brevity, thehydrocarbon analyzer will be referred to in the following descriptionand accompanying drawings simply as an "octane monitor.

An octane monitor based on a stabilized cool flame generator possessesnumerous advantages over conventional octane number instruments such asthe CFR engine or automated knock-engine monitoring systems. Among theseare: elimination of moving parts with corresponding minimal maintenanceand down-time; high accuracy and reproducibility; rapid speed ofresponse providing a continuous, real-time output; compatibility ofoutput signal with computer or controller inputs; ability to receive andrate gasoline samples of high vapor pressure, e.g., up to as high as 500psig., as well as lower vapor pressure samples (5-250 psig.). Thesecharacteristics make the octane monitor eminently suitable not only foran indicating or recording function, but particularly for a processcontrol function wherein the octane monitor is the primary sensingelement of a closed loop control system comprising zero, one, two ormore subloops connected in cascade.

DESCRIPTION OF The PRIOR ART Typical of such a hydrocarbon conversionprocess is catalytic hydroreforming, wherein a naphtha fraction ispassed into a reaction zone containing a noble metal catalyst, in thepresence of a molor excess of hydrogen. The basic processing techniqueand a preferred catalyst are indicated in U.S.- Pat; Nos.- 2,479,l09 and2,479,110, issued to Vladimir I-I'aensel, wherein the catalyst comprisesalumina, platinum, and halogen. Re forming is undertaken at atemperature in the range of from about 600 F. to about l,l00 F.; at apressure in the range of from about psig. to about] ,000 psig.,

but more normally in the range of from about 200 to about 500 psig.; ata liquid hourly space velocity in the range of from about 0.5 l/hour toabout l0.'0 l/hour; and in the presence of from about 0.5 to about 10.0moles of hydrogen per mole of hydrocarbon.

As understanding of the reaction mechanisms occurring within thereforming zone has increased, it has become possible to adjust operatingtechniques and catalyst compositions to enhance the specific reactiondesired. Thus, it is a primary purpose of catalytic reforming to subjecta substantially sulfur, nitrogen, oxygen, olefin, and metal freegasoline boiling range or naphtha boiling range charge stock to hightemperature and pressure in the presence of hydrogen in 'order toenhance the anti-knock properties of the hydrocarbons contained therein.It has been determined that such enhancement, resulting in a high octanegasoline product, is derived from four specific chemical reactions; (1)the dehydrogenation of naphthenic hydrocarbons to produce thecorresponding aromatic derivative, (2) the dehydrocyclization ofparaffinic hydrocarbons to produce corresponding aromatic hydrocarbons,(3) the hydrocracking of high molecular weight hydrocarbons to producelower molecular weight hydrocarbons, and (4) the isomerization of normalparaffinic hydrocarbons to produce branched chain isomers of equalmolecular weight.

Each of these four reaction mechanisms upgrade low octane hydrocarbonsto high octane hydrocarbons, but as the automotive manufacturershaveincreased engine compression ratios it has become necessary toadjust operating techniques in order to control the reaction mechanismsselectively to maximize octane with minimum loss of liquid product yieldand minimum production of paraffinic gas (methane, ethane, and propane).It has thus been determined that the dehydrogenation of naphthenes toaromatics is promoted by operating at lower pressure levels; thatdehydrocyclization of paraffins to aromatics is promoted by low pressureand high temperature; that. hydrocracking of paraffins is promoted byhigh pressure, high temperature, and high residence time of the chargestock on the catalyst; and that isomerization of paraffins is promotedby intermediate temperature, and a catalyst comprising a much higherhalogen content than normally employed. Since aromatic hydrocarbons havehigher octane ratings than other hydrocarbonsof equivalent molecularweight, catalytic reforming has showed a current tendency to operate athigher temperatures and lower pressures in order to enhance theresulting gasoline octane rating by increasing the aromatic hydrocarboncontent of the gasoline. Therefore, the catalyticreforming unitproducing high octane motor fuel, typically is maintained at operatingconditions sufficient to enhance the dehydrogenation of naphthenes andthe dehydrocyclization of paraffins in order to maximize the productionof both aromatics and hydrogen, maximum hydrogen being desired since itis normally consumed elsehere in the typical petroleum refinery. Theproduction of aromatic hydrocarbons is enhanced by catalytic reformingat a temperature in the range of from about 850 F. to about l,050 F. andat a pressure in the range of from about 100 psig. to about 400 psig.when the end boiling point of the charge stock is about 350 F., but whenthe end point of the charge stock is about 400 F. or more, the preferredpressure is about 500 psig. in order to maintain catalyst stability.

The operator of the catalytic reforming unit judi ciously selects theoperating conditions which he believes will most economically producethe desired high octane gasoline. The naphtha charge stock is passedinto the reaction zone under conditions of temperature, pressure,catalyst composition, hydrogen to hydrocarbon ratio, etc., which willproduce a reactor effluent having the composition necessary to result inthe desired high octane product. When analysis indicates that theproduct does not meet octane specification, it is normal in the art forthe operator to manually change conditions within the reaction zone tocompensate for any deviation from specification.

The resulting hot vaporous reactor effluent containing hydrogen,normally gaseous hydrocarbons and gasoline boiling range hydrocarbons iswithdrawn from the reaction zone, cooled, condensed, and passed to aseparation zone which is normally a single stage gravitytype phaseseparator maintained at reforming pressure of, say, 50-500 psig. Theliquid hydrocarbon or unstabilized reformate phase is in equilibriumtherein with the gas phase containing a major proportion of hydrogen.The hydrogen-rich vapor phase is withdrawn and a portion thereof isrecycled to the inlet of the catalytic reforming zone for circulationacross the catalyst together with the naphtha charge. The liquidhydrocarbon phase from the separator is then ultimately fed to adistillation zone which normally comprises a stabilizer column. Theliquid phase contains a substantial portion of dissolved hydrogen and C-C hydrocarbons which must be removed in order that the stabilizedreformate will meet vapor pressure and octane number specifications. Atypical sample of catalyticreformate from a separator operating at 250psig. consists of:

Component Mol 2.5 i 0.5

The overhead from the stabilizer column is predominently C and lighterhydrocarbonsand the column bottoms is stabilized gasolinetypically'comprising predominantly C to about 400 F. endpoint material.

By and large it has been the practice to operate the catalytic reformingunit mostly in the dark so far as octane number of the stabilizedgasoline product is concerned. That is to say, the stabilizer columnbottoms is manually sampled perhaps once every 8-hour shift or perhapseven only once a day. The samples are picked up and taken to thelaboratory where each sample is run and the result is then transmittedback to the unit operator who, untilthen, has not been able to ascertainwhat change, if any, should have'been 'made at the time the sample wastaken. K

Therefore, to be on the safe side, the unit operator will usually runthe reforming reaction zone with excessive heat input in order toguarantee that the octane quality of the reformate gasoline will meetspecification. The net result is that the resulting stabilized reformatewill actually exceedxproduct specifications with respect to octane agood part of the time. This mode of operation increases the refinerscosts since, as those skilled in the art know, decrease in product yieldaccompanies increase in product octane number.

The control problem is further complicated by the not uncommon practiceof using'a single stabilizer column to process more than onegasolinestream. For example, a single stabilizer column will often receiveplural or combined feeds which may comprise unstabilized reformates fromtwo or more independently operated catalytic reforming units. An upsetin the operation of a single such reformer will carry through to thestabilizer and be reflected in off-specification product so that thestabilizer bottoms product is no longer indicative of only the operationof a single reformer.

Continuously meeting octane number specification is, thus, anexceedingly difficult and haphazard task when employing a singlestabilizer column to handle a plurality of gasoline streams. When theoctane number of the stabilizer bottoms falls below the specificationlevel, it often is not possible to determine which of the pluralunstabilized reformate feeds to the column is the source of the lowoctane number gasoline boiling range hydrocarbon components in the finalstabilized gasoline product, If product. reaction severity is increasedat the wrong reforming unit, there is the danger that the resultingyield loss will far outstrip the resulting value of octane enhancementfor the combined stabilized gasoline.

In addition, it is often found that the stabilizer bottoms fraction doesnot meet the octane number specification despite the fact that thecatalytic reforming unit is operating properly. When such a condition isnot recognized, remedial steps may be taken at the reaction zone with nocorresponding remedial result being obtained in the octane number of thestabilized gasoline product. The result may later be found to be causedby misoperation of the stabilizer column. Or the result may later befound to be caused by the introduction of extraneous material into thestabilized gasoline product, as when it is found that the stabilizerreboiler is leaking hot oil heating medium into the gasoline product. I

Various schemes have been experimented with to control the reactionseverity of a continuous hydrocarbon conversion process to obtain a moreefficient operation. Typical of such schemes is set out in Uj.S Pat.3,497,449 issued to RJ. Urban on Feb. 24, 1970. In that particularpatent an octane number monitor of a CFR engine type is shown to beincorporated in a reforming process stream. The use of a CFR engine typemonitor is not a practical means to control a continuous hydrocarbonconversion process. Such a device cannot operate at elevated pressures,and the samples to be monitored must be degassed or otherwise stabilizedbefore injection into the monitor. This adds to the analytical lap timethat is inherently long to begin with. lt is extremely difficult toachieve and maintain any control stability with such a device. itappears from the general context of the Urban patent that the use of theCFR octane monitor is not so much in the direct controlling of aprocess, but, on the contrary, for use in long term analysis of aparticular process so that empirical data may be obtained for use incontrolling that process.

Another prior art scheme is set out in US. Pat. 3,000,812 issued to D.M.Boyd, Jr. on Sept. 19, 1961. In this particular scheme an octanemeasuring device is used to analyze the product issuing from thefractionator which as set forth above is located downstream oftheseparation zone in the reforming process scheme. The data obtainedfrom this octane monitor was contemplated to have a transport lap timeand response time of a significant amount. This was the basic reason forusing the particular cascade system described in the Boyd patent.

The language of the Fe-nske patent described above indicates that themonitor of that invention may be used as means for detecting compositionchanges, and for supplying information as to the required direction andmagnitude of corrective action to be applied to a control processcondition in order to restore the sample composition to specifications.Nowhere in the teachings of the Fenske patent does there appear languageto the effect of continually controlling a hydrocarbon conversionprocess by utilizing a control signal derived from a liquid sample of avapor-liquid phase separation zone without intervening depressurizationof the liquid to control such a process. The Urban patent appears todisclose this feature; however, as mentioned above the octane monitor ofthe Urban patent must be supplied with a stabilized product whichinherently means that the liquid product from the separation zone of theUrban scheme must be stabilized and depressured.

SUMMARY OF THE INVENTION for use in adjusting and controlling conversionseverity in a manner sufficient to provide a hydrocarbon product havinga constant predetermined level of quality.

It is a particular object of the present invention to provide such animproved continuous monitoring and control system for use in varyingheat input to a reaction zone, responsive to the octane number of theeffluent liquid hydrocarbon discharged from the reaction zone, wherebythe octane number'of the ultimate gasoline product is maintained at aconstant predetermined level.

These and other objects of the present invention, as well as theadvantages thereof, will be more clearly understood as the invention ismore particularly disclosed hereinafter.

In accordance with the present invention, the octane monitor comprisinga stabilized cool flame generator with servo-positioned flame front isconnected to receive a continuous sample of the liquid phase of thereactor effluent, directly from the vapor-liquid separator of thereforming reaction zone without intervening depressurization below theseparator pressure. Since the liquid phase sample which is sent to thecombustion chamber of the octane monitor-thusremains at substantiallythe reaction zone pressure, the samplecontains not only the normallyliquid hydrocarbon constituents comprising the final gasoline p'roduct,but also a substantial amount of dissolved high vapor pressureconstituents, normally comprising dissolved hydrogen and normallyvaporous hydrocarbons such as methane, ethane, and propane. However, theoutput signal of the octane monitor can be, and preferably is,calibrated directly in terms of octane number, notwithstanding thepresence of a substantial portion of high'vapor pressure constituentswithin the sample. The output signal from the octane monitor is thenutilized to reset or adjust heat input to the reaction zone so that theoctane number of the liquid phase of the reactor effluent is maintainedat a substantially constant predetermined level.

The inventive control system thus assures that the liquid phase of thereactor effluent (the unstabilized reformate gasoline being fed to thestabilizer column) will always remain on specification, relative tooctane number, regardless of external upsets or disturbances. Thecontrol system thus effects a savings in utility cost in that since theoctane number is continuously monitored, the reaction zone is therebycontinuously operated at a minimum heat input. Raw material cost is alsominimized since minimum heat input minimizes the conversion severity andthereby results in a minimum loss of product yield to obtain a gasolineproduct of substantially constant octane number.

Because there is a direct measurement and control of the octane ratingof the unstabilized refonnate gasoline, this control system is tobedistinguished from those prior art control systems wherein somecomposition property such as percent aromatics, or conductivity, ordielectric constant, is measured and controlled. All of these latterphysical properties are merely an indirect indication of octane ratingwhich is only narrowly correlatable therewith. Such indirect correlationbecomes invalid for any significant deviation from the design controlpoint.

i The control system of this invention is also to be distinguished fromthose prior art systems employing automated knock-engines as the octanemeasuring device, such as shown in the Urban patent referred to above.Since the octane monitor utilized within the inventive control systemcomprises a stabilized cool flame generator, it is normal to introducethe sample directly into the octane monitor substantially at theseparator or reaction zone pressure (separator pressure equals reactionzone pressure less the pressure drop through heat exchange equipment andpiping). The sample therefor contains a substantial amount of dissolvedhydrogen and normally gaseous hydrocarbon vapors within the liquidphase, and such a sample obviously cannot be sent directly to anautomated knockengine type of octane measuring device. The knockcnginescannot operate at elevated pressures, and the samples thereto must bedegassed or otherwise stabilized before injection into the knock-enginesince a high vapor pressure sample may vapor lock a knockengine type ofoctane measuring device.

The control system of this invention is further to be distinguished fromthe prior art systems employing automated knock-engines as the octanemeasuring device in that the instant octane monitor is compact in size,can be totally enclosed by an explosion proof housing, and therefore canbe used in hazardous locations. As a matter of fact, the octane monitorof the present invention is typically field installed immediatelyadjacent to the reaction zone vapor-liquid separator in order tominimize the run of high pressure tubing conducting the sample of liquidhydrocarbon phase to the combustion chamber of the octane monitor. Aknock-engine in contrast cannot be employed in hazardouslocations andmust therefore be situated remote from the sample point. I

The sample transport lag ordead time of a close coupled octane monitoras employed within the scope of the present invention is typically ofthe order to 2 minutes or less, and its 90 response time is another 2minutes. This provides a very good approach to an essentiallyinstantaneous or real time output. By way of contrast, the transport andresponse lags alone of a knock-engine as disclosed in the Urban patentmay be of the order of 30 minutes or more, which those skilled in thecontrol system art will recognize to be a substantial departure fromreal time output. With that much dead time built into a closed loop itis extremely difficult to achieve and maintain control stability, andundampened cycling may result. Particularly is this true in the systemof the present invention since the sample being sent directly to theoctane monitor would have to first be degassed before such liquid couldbe injected into the knock-engine. Any nonequilibrium or inconsistentdegassing will introduce an additional uncontrollable disturbance intothe control system since the degassed sample will not be trulyindicative of the reactor effluent composition or octane number.

In a broad embodiment it may, therefore, be summarized that the presentinvention comprises a control system for use and in combination with acontinuous flow hydrocarbon conversion process wherein a hydrocarboncharge stock is passed through a conversion zone at conversionconditions comprising elevated temperature, and the resulting conversionproduct effluent is separated into a vapor phase and into a liquid phasecomprising gasoline boiling range hydrocarbon components, saidconversion process having charge stock preheating means, said conversionzone, a vaporliquid phase separation zone, first conduit means forpassing charge stock to said preheating means, second conduit means forpassing charge stock from said preheating means to said conversion zone,third conduit means for passing conversion product effluent from saidconversion zone to said separation zone, and means for supplying heat tosaid preheating means from an external source, the improved controlsystem for said conversion process comprising in combination; (a)operatively associated with said heat supplying means, means to vary theheat input to said preheating means; (b) a hydrocarbon analyzercomprising a stabilized cool flame generator with a servo-positionedflame front, continuously receiving a sample of said liquid phase fromsaid separation zone, and developing an output signal which in turnprovides a measure of sample octane number; and, (0) means transmittingsaid analyzer output signal to said heat input varying means whereby theheat input to said preheating means is regulated responsive to octanenumber of said liquid phase and said octane number is thereby maintainedat a constant predetermined level.

Preferred specific embodiments of the present invention will incorporateone or more cascaded subloops which more immediately control the heatinput to the reation zone. For example, where the reaction zone isindirectly heated by a fluid heating medium such as combusition gas,steam, reactoreffluent, or hot oil, there may be a flow control loop onthe heating medium to the reactor preheater, the octane monitor outputthen being cascaded to the flow controller setpoint. Alternatively, areactor inlet temperature control in strument may reset the flowcontroller and the octane monitor output may reset the temperaturecontroller setpoint. Other embodiments will become apparent in light ofthe detailed description of the invention which follows.

The invention may now be more clearly understood by reference to theaccompanying figures which set forth a simplifiedschematic flow diagramof a typical catalytic reforming reactor system in which particularembodiments of the inventive control system are utilized.

FIG. 1 illustrates a catalytic reforming unit wherein the heat input tothe reaction zone preheater is controlled by cascading the octanemonitor output signal to a temperature controller which then sends asignal to reset a flow controller on the heating medium.

FIG. 2 illustrates a triple cascade system for regulating the heat inputto the reaction zone by sending the octane monitor output signal to adifferential temperature controller which in turn resets the reactorinlet temperature controller which in turn resets the flow controller onthe heating medium.

FIG. 3 illustrates a further embodiment wherein the octane monitor reseta differential temperature controller which in turn resets the flowcontroller on the heating medium.

DESCRIPTION OF THE FIGURES With reference now to FIG. 1 there is shown asimplified schematic flow diagram for a typical catalytic reformingunit. A low octane number charge stock comprising naphtha or gasolineboiling range, hydrocarbon constituents having an end boiling point ofabout 350 F. enters the reforming process via line I. A recycle gasstream is injected into line 1 via line 2. This gas stream comprisespredominantly hydrogen, with a minor portion of normally gaseoushydrocarbon vapor comprising methane, ethane, and propane, with tracesof heavier hydrocarbons. The resulting mixture of hydrogen andhydrocarbon passes into a reactor preheater 3 via line 1. Preheater 3may be any type of heat exchanger employing any type of heating mediumsuch as steam, hot oil, hot vapor, flue gas, etc. Normally, however, inorder to achieve the high temperature required, preheater 3 will be adirect fired furnace as illustrated. The reaction mixture of hydrogenand hydrocarbon is heated within coil 4 in preheater 3. Coil 4 istypically placed in the radiation section and the convection section ofthe preheating furnace 3.

The heated reaction mixture leaves preheater 3 via line 5, typically ata temperature of from about 900 F. to l,000 F. depending upon thecomposition of the hydrocarbon feed stock.'The hot mixture passes into areaction zone comprising at least one reactor vessel 6 at a pressure ofabout 300 psig. The reaction zone contains a noble metal reformingcatalyst and the reaction mixture undergoes a conversion to lowerboiling hydrocarbon constituents having a higher octane number. Thereaction primarily comprises dehydrogenation of naphthenes which is anendothermic reaction. Consequently, the reaction mixture leaves thereaction zone via line 7 at a temperature typically from 20 to 150 F.below the reactor inlet temperature, depending upon the naphthenecontent of the charge stock.

The reactor effluent passes via line 7 into a heat exchanger 8 whereinthe mixture is cooled and normally liquid constituents are condensed.The condensed and cooled mixture leaves the heat exchanger 8 at atemperature of about 60 -l 20 F., and passes into a separator 10 vialine 9. Separator 10 will be at a pressure which is substantially thesame pressure as the reaction zone, but it will be at a slightly lowerlevel due to pressure drop through the reactor catalyst bed, line 7,heat exchanger 8, and line 9. Thus, whereas reactor 6 will typically beat an inlet pressure of about 300 psig., separator 10 will typically beat a pressure of about 250 psig.

The condensed and cooled effluent entering separator 10 via line 9 isseparated therein into a vapor phase and a liquid phase. The vapor phaseis withdrawn via line 2 for recycle to the reaction zone inlet.Compressor means, not shown, sends the hydrogen-rich vapor phase vialine 2 into line 1 for mixture with the charge stock, as was previouslyset forth hereinabove. The catalytic reforming raction not only upgradesthe hydrocarbon constituents to higher octane number components but italso produces hydrogen as a byproduct of the process. Consequently, anet hydrogen-rich gas is withdrawn via line 11 by conventional pressurecontrol means, not shown, as a net gas product which is typically sentto further processing units for consumption elsewhere in the refinery.

The liquid phase of the reactor effluent will have a component analysissimilar to that presented hereinabove. The liquid phase containingdissolved gaseous components is withdrawn from separator 10 via line 12,and is passed through a control valve 13 and line 14, usually into afractionation zone, not shown. The liquid phase withdrawal ratetypically is adjusted by a liquid level contr'ller 15 which may beoperated by a level sensing means 16, such as a float mechanism,dielectric probe, DP cell, or other similar level sensing means. Thelevel controller 15 adjusts valve 13 by transmitting a pneumatic,electrical, or hydraulic output signal thereto via line 17.

Heat input to the raaction zone is provided by introducing a fuel vialine 18 into a bank of combustion nozzles 19 within the furnace 3. Thefuel,- which may be liquid or gas, is burned within the combustion zoneand the hot combustion gas passes through the furnace and out the stack.As the fuel is burned and the combustion gas passes through the furnace,it imparts the necessary heat input into the reaction mixture containedwithin the coil 4 by means of radiation and convection. The heat inputinto the reaction mixture is controlled and adjusted by varying the flowof fuel to the bank of combustion nozzles 19. The control of the flow offuel is achieved by means of a flow control loop contained in line 18.The flow control loop comprises a control valve 20 and a flow sensingmeans 24, which for illustrative purposes is shown as an orifice. A flowsignal line 23 transmit the flow signal from orifice 24 to flowcontroller 22. Flow controller 22 then transmits an output signal to thecontrol valve 20 via line 21. The setpoint of flow controller 22 isautomatically adjustable.

A temperature controller 26, also with an automatically adjustablesetpoint, senses the reactor inlet temperature as detected by athermocouple or other sensing means 27 located in the reactor inlet line5or in any other suitable inlet portion of the reaction zone. Theresultingtemperature output signal is transmitted from temperaturecontroller 26 to flow controller 22 via line 25 to adjust or reset thesetpoint of flow controller 22. Octane monitor 28 utilizing a stabilizedcool flame generator with servo-positioned flame front is fieldinstalled immediately adjacent to separator 10. In a preferredembodiment, the flows of oxidizer (air) and fuel (effluent liquid phasesample) are fixed, as in the induction zone temperature. Combustionpressure is the parameter which is varied in a manner to immobilize thestabilized cool flame front. Upon a change in sample octane number, thechange in pressure required to immobilize the flame front within theoctane monitor provides a direct indication of the change of octanenumber in the sample delivered to the combustion chamber. Typicaloperating conditions for the octane monitor are:

Air Flow Fuel Flow Induction Zone Temperature 3500 cc/min. (STP) lcc/min.

700F. (Research Octane) 800F. (Motor Octane) Combustion Pressure 4-20psig.

Octane Range (Max.) -102 The actual calibrated span of the octanemonitor as here utilized will, in general, be considerably narrower. Forexample, if the target octane is clear (research method), a suitablespan may be 92-98 research octane. When a relatively narrow span isemployed, the octane number change is essentially directly proportionalto the change in combustion pressure.

Dashed line 29 represents a suitable sampling system to provide acontinuous sample of the liquid phase of the reactor effluent to theoctane monitor. The sample is withdrawn from separator 10 or from line12 upstream of control valve 13 and passed into the octane monitorwithout intervening depressurization. The sample system may comprise asample loop taking a liquid sample at a rate of cc. per minute from apoint The octane monitor output signal is transmitted via line 30 to thesetpoint of the temperature controller 26. This may be a direct fieldconnection but preferably the octane monitor output will first be sentto an octane controller recorder located in the refinery control houseand the control signal therefrom is then sent to reset the setpoint oftemperature controller 26 which may also be a temperature recordingcontroller located in the control house.

Upon a decrease in the measured octane number of the liquid phasesample, the octane monitor will call for an increase in the reactionzone temperature in order to dehydrogenate a greater proportion of thenaphthanes in the charge stock, to produce a greater amount of highoctane aromatic hydrocarbon in the effluent. Temperature controller 26then will call for an increase in the flow of fuel to the preheater 3 inorder to increase the heat imput into the reactants in coil 4, andthereby increase the temperature of the reaction mixture entering thereaction zone.

If the octane number of the effluent sample is higher than the requiredspecification, the octane monitor will call for a decrease in thereaction zone temperature and the overall corrective action will be thereverse of that previously described. In either event the octane numberof the liquid phase of the reactor effluent is continuously monitoredand the reaction zone is controlled, under conversion conditionssufficient to provide a substantially constant octane number on theliquid phase of the effluent at a constant predetermined level.

It is well known to those skilled in the art that the overall heat ofreaction for catalytic reforming is endothermic. That is to say, thetemperature of the effluent leaving the reaction zone will be asubstantial number of degrees below the temperature of the reactantmixture entering the reaction zone. The difference in temperaturebetween inlet and outlet of the reaction zone is typically utilized asan indication of the reaction severity or as an indication of the degreeand type of reaction occurring within the reaction zone. While theindicated temperature difference is an indication of the reactionseverity it is not a direct indication of the resulting octane number ofthe liquid hydrocarbon components being produced within the zone.However, it is often desirable to monitor this temperature differenceacross the reactor with a differential temperature indicator.

Accordingly, there is indicated in FIG. 2 a further preferred embodimentof the present invention wherein the control system employing the octanemonitor, comprising a stabilized cool flame generator withservo-positioned flame front, also incorporates a differentialtemperature control instrument. FIG. 2 illustrates the typical schematicflow diagram of a catalytic reforming unit which is identical to theunit illustrated in FIG. I and described hereinabove.

Referring now to FIG. No. 2 there is again shown the flow control loopon the fuel line 18 feeding the reaction zone preheater 3. The flowcontrol loop comprises the flow control valve 20 receiving an outputsignal via line 21 from flow controller 22. Flow controller 22 receivesthe flow rate signal from sensing means 24 via the flow signal line 23.Flow controller 22 has an adjustable setpoint which again is reset bythe output signal of temperature controller 26, said output signal beingtransmitted via line 25. Temperature controller 26 receives atemperature signal from the inlet of the reactor 6 by means of atemperature sensing device such as thermocouple 27. Temperaturecontroller 26 also has an adjustable setpoint.

On the inlet to the reactor 6 there is shown another temperature sensingmeans such as thermocouple 31, which may be located in line 5 or in aninlet section of reactor vessel 6 or of the catalyst bed containedtherein. On the outlet of the reactor 6 there is additionally shown atemperature sensing means such as thermocouple 32, which may be locatedin line 7 or in an outlet section of reactor vessel 6 or of the catalystbed contained therein. Temperature sensing means 31 and 32 send thetemperature singals to a differential temperature controller 33 havingan automatically adjustable setpoint. The difference temperaturecontroller 33 senses the temperature difference across the reactionzone. Temperature controller 33 develops an output signal which resetsthe automatically adjustable setpoint of temperature controller 26 bymeans of a transmitting line 34.

As the liquid portion of the hydrocarbon effluent from the reaction zoneis sampled by octane monitor 28 by means of sampling loop 29, octanemonitor 28 develops an output signal which is transmitted via line 30 tothe automatically adjustable setpoint of the differential controller 33.As the octane monitor 28 receives a sample which is below the requiredoctane number for the liquid phase of the reactor effluent, the monitorresets the automatically adjustable setpoint of differential controller33 in order to increase the temperature difference between inlet andoutlet of the reactor. The increase in temperature difference is adirect indication of an increase in the degree of dehydrogenation ofnaphthenes, and thereby indicates that high octane number aromaticconstituents are being produced in greater amount. In order to increasethis temperature difference across the reaction zone, differentialtemperature controller 33 sends a signal via controller output line 34to temperature controller 26, and resets the automatically adjustablesetpoint thereto in order to increase the inlet temperature to reactor6. Temperature controller 26 in turn develops a controller output signalwhich is sent via line 25 to the automatically adjustable setpoint offlow controller 22. The output signal from temperature controller 26readjusts the setpoint of flow controller 22 in order to open controlvalve 20 and thereby introduce more fuel into the bank of nozzles 19 foradded combustion and a greater heat input into the reaction mixture.

When the liquid hydrocarbon effluent which is sampled via sample loop 29indicates that the octane of the effluent being produced is too high,the octane monitor 28 will send an output signal via line 30 to theautomatically adjustable setpoint of differential temperature controller33 calling for a reduction in the-temperature drop across the reactionzone. The reduction in temperature drop is an indication of a reductionof dehydrogenation of naphthenes and thereby indicates that the octanenumber of the resulting effluent will be reduced. In order to accomplishthis temperature reduction, differential temperature controller 33 willcall for a reduction of inlet temperature by sending an output signalvialine 34 to readjust the setpoint of the temperature controller 26 toa lower temperature level. Temperature controller 26 in turn sends acontroller output signal via line 25 to the automatically adjustablesetpoint of flow controller 22 to reset the flow of fuel via line 18into combustion nozzles 19. The lower fuel flow rate reduces the rate ofthe heat input into the reaction mixture and the inlet temperature tothe reactor is thereby reduced.

While the triple cascade system illustrated in FIG. 2 represents apreferred embodiment, it is within the scope of this invention to omitthe temperature controller 26 and to reset flow controller 22 directlyby the output signal of the differential temperature controller. Thismodified embodiment is illustrated in FIG. 3.

Referring now to FIG. 3 there is again shown the differentialtemperature controller 33 receiving an inlet temperature signal by meansof thermocouple 31 and an outlet temperature signal by means ofthermocouple 32. The controller output signal is transmitted via line 34to the automatically adjustable setpoint of the flow controller 22.

When the sample of the liquid phase of the hydrocarbon effluent passingvia line 29 into octane monitor 28 indicates that the octane is too low,the octane monitor will send an output signal via line 30 to theautomatically. adjustable setpoint of differential temperaturecontroller 33 calling for an increase in the temperature differenceacross the reaction zone. In order to achieve this increase intemperature difference the inlet temperature of the reaction zone 6 mustbe increased, as evidenced by .a temperature indicator 41 receiving asignal from a temperature sensing means such as a thermocouple 40. Thoseskilled in the art realize, of course, that indicator 41 is notessential to effect control, but is typically provided for conveniencein monitoring temperature. Differential temperature controller 33 sendsan output signal via line 34 to flow controller 22 toopen control valve20 and thereby increase the flow of fuel via line 18 into the bank ofcombustion nozzles 19. A greater heat input is thereby imparted to thereaction mixture in coil 4 and the temperature of the incoming feed tothe reaction zone is thereby increased. The increased temperature levelon the inlet of reactor 6 will precipitate a greater temperaturedifference since the increased inlet temperature creates a greater rateof reaction for the dehydrogenation of naphthenes and the other octaneenhancing reactions occurring within the catalyst bed.

When the octane of the liquid sample passing into octane monitor 28 vialine 29 is greater than is required, the octane monitor 28 will transmitan output signal via line 30 which adjusts the automatically adjustablesetpoint of differential temperature controller 33 to reduce thetemperature difference across the reaction zone. The differentialtemperature controller 33 then sends an output signal via line 34 to theautomatically adjustable setpoint of flow controller 22 in order toreduce the flow of fuel into the preheater combustion nozzles 19. Thereduction of preheat input into the reaction mixture will produce adecrease in the inlet temperature as shown by temperature indicator 41which indicates the temperature as sensed by the thermocouple 40. Thereduction of the inlet temperature produces a decrease in the rate ofreaction ,within the reac tion zone as evidenced by a decrease in thetemperature drop across the catalyst bed. The resulting effluentleaving. separator 10 via line 12 will then have a decreased octanenumber.

PREFERRED EMBODIMENTS While the multiple cascade arrangementsillustrated in FIGS. 1 through 3 represent preferred embodiments, it iswithin the scope of this invention to omit the temperature controller 26and the differential temperature controller 33 and to reset flowcontroller 22 directly by the octane monitor output signal transmittedvia line 30. Similarly, flow controller 22 could be eliminated, in whichcase temperature controller 26 and/or differential temperaturecontroller 33 would send their respective output signals directly tovalve 20. Alternatively, the flow controller 22, temperature controller26, and differential controller 33 could be eliminated, in which caseoctane monitor output signal line 30 would connect directly with valve20. It may be expected, however, that elimination of either or both ofthe temperature control subloops will obviously result in a pooreroverall control system. Since the octane number of the hydrocarboneffluent is not correlatable with the flow of fuel to the preheater, butis correlatable with the inlet temperature of the reaction zone and withthe temperature drop across the reaction zorie, it is obvious to thoseskilled in the art that the temperature controller 26 and/or thedifferential temperature controller 33 should be included in the'controlsystem for optimum control.

The method of operation of the invention control system is readilyapparent to those skilledin the art from the foregoing discussionrelative to the figures. In addition, the advantages of the presentinvention are equally apparent. f

The primary advantage is that the present invention provides an improvedcontinuous monitoring and control system for use in varying heat inputto a reaction zone, responsive to the octane number of the effluentliquid hydrocarbon discharged from the reaction zone, whereby the octanenumber of the ultimate gasoline product is maintained at a constantpredetermined level. In particular, reaction severity is controlled toproduce a hydrocarbon product having a constant predetermined level ofquality despite operational upsets and control system deviations whichmay occur external or internal to the catalytic reforming unit. Forexample, the inventive control system allows the petroleum refiner toproduce a reformate gasoline product of constant octane despitevariations in charge stock composition or changes in catalyst activity.

An additional advantage is that since the control system is proximate tothe reaction zone the response time between a change in reactionseverity and a change in sample octane number is a matter of minutes. Onthe other hand, if the sample sent to the octane monitor is a stabilizedgasoline sample from the fractionation zone, the intervening fractionaldistillation equipment introduces a substantial time lag between achange in reaction zone conversion conditions and the correspondingchange in octane number of the finished product.

As used herein, the terms reaction zone and conversion zone are held tobe equivalent terms. Similarly, the terms reaction conditions" andconversion conditions are used interchangeably. However, the termsseparator and separation zone have a limited definition in accordancewith the teachings presented hereinabove. In the instant invention theliquid sample is withdrawn from a vapor-liquid phase separator whichthose skilled in the art know to be readily distinguishable from anycomponent separator or separation zone such as a distillation column orzone.

In the foregoing disclosure the use and application of the improvedcontrol system has been disclosed with reference to a catalyticreforming system. Those skilled in the art realize, however, that theinventive control system is not so limited. The inventive control systemwhich has been disclosed hereinabove may be utilized in any hydrocarbonconversion process wherein a resulting product effluent is separatedinto a vapor phase and a liquid phase comprising gasoline boiling rangehydrocarbon constituents such as thermal cracking, catalytic cracking,thermal hydrocracking, catalytic hydrocracking, isomerization,alkylation, polymerization, etc., which have such a separation zone.

Similarly, the simplified process flow drawings of the figures disclosea single preheater and a single reactor vessel. Those skilled in the artrealize that many conversion processes employ plural reactor vesselswith a preheater at each individual reaction vessel. Thus it is withinthe scope of the present invention to apply an embodiment of theinventive control system at more than one of a plurality ofpreheater-reactor combinations. For example, catalytic reformingtypically employs three or more reactor vessels and correspondingpreheaters. For a three reactor catalytic reforming unit then, apreferred application would be to monitor the separator liquid as taughthereinabove, and transmit the octane monitor output signal via threeindividual output signal lines to an independent cascaded control systemof the type disclosed herein at each of the three preheater-reactorcombinations. The method of adapting the present invention to providemultiple applications of the inventive control system, will be readilyapparent to those skilled in the art utilizing the teachings which havebeen presented hereinabove.

Additionally, while the inventive control system has been disclosed withreference to the control of conversion or reaction severity by theadjustment and control of heat input, those skilled in the art realizethat the inventive control system may be utilized to control severity bythe adjustment of any other operating variable. For example, in fluidcatalytic cracking the inventive control system may be utilized tocontrol the rate of catalyst circulation. In HF Alkylation the inventivecontrol system may adjust reaction severity by adjustments to the rateof circulation of isobutane reactant. ln polymerization over solidphosphoric acid catalyst, the inventive control system may adjustreaction severity by adjusting the rate of flow of olefin reactant tothe reaction zone. In each instance, the adjustments to the conversionor reaction severity made by the inventive control system, will resultin the production of an ultimate gasoline product having an octanerating more easily maintained at a constant specification value.

We claim:

1. ln a continuous flow hydrocarbon conversion process wherein ahydrocarbon charge stock is passed through a conversion zone atconversion conditions comprising elevated temperature, and the resultingconversion product effluent is separated into a vapor phase and into aliquid phase comprising gasoline boiling range hydrocarbon components,said conversion process having charge stock preheating means, saidconversion zone, a vapor-liquid phase separation zone, means for passingcharge stock to said preheating means, means for passing charge stockfrom said preheating means, to said conversion zone, means for passingconversion product effluent from said conversion zone to said separationzone, and means for supplying heat to said preheating means from anexternal source, the improved control system for said conversion processwhich comprises in combination:

a. operatively associated with said heat, supplying means, means to varythe heat input to said preheating means;

b. a hydrocarbon analyzer comprising a stabilized cool flame generatorwith a servo-positioned flame front, continuously receiving a sample ofsaid liquid phase from said separation zone without interveningdepressurization, and developing an output signal which in turn providesa measure of sample octane number; and,

c. means transmitting said analyzer output signal to said heat inputvarying means whereby the heat input to said preheating means isregulated responsive to octane number of said liquid phase and saidoctane number is thereby maintained at a constant predetermined level.

2. The system of claim 1 wherein said heat input varying means comprisesa flow control loop including a flow controller having an adjustablesetpoint regulating the flow of heating medium through said preheatingmeans, whereby said setpoint is adjusted in response to said analyzeroutput signal.

3. The system of claim 2 further characterized in the provision of meansto sense conversion zone temperature, temperature control meansconnecting with said temperature sensing means with such control meanshaving an adjustable setpoint and developing a temperature outputsignal, and means transmitting said temperature output signal to thesetpoint of said flow controller, with said means (c) transmitting saidanalyzer output signal to said temperature control means setpointwhereby the latter is adjusted responsive to liquid phase octane number.

4. The system of claim 3 wherein said temperature sensing meanscomprises first means sensing the temperature of an inlet section ofsaid conversion zone and second means sensing the temperature of anoutlet section of said conversion zone, whereby said temperature outputsignal provides a measure of temperature difference between said inletand outlet sections.

5. The system of claim 2 further characterized in the provision of firstmeans to sense a first temperature of said conversion zone, firsttemperature control means connecting with said first temperature sensingmeans with such control means having an adjustable setpoint anddeveloping a first temperature output signal, means transmitting saidfirst temperature output signal to the setpoint of said flow controller,second means to sense a second temperature of an inlet section of saidconversion zone, third means to sense a third temperature of an outletsection of said conversion zone, second temperature control meansconnecting with said second and third temperature sensing means withsuch control means having an adjustable setpoint and developing a secondtemperature output signal which provides a measure of temperaturedifference between said inlet and outlet sections, and meanstransmitting said second temperature output signal to the setpoint ofsaid first temperature control means, with said means (c) transmittingsaid analyzer output signal to said second temperature control meanssetpoint whereby the latter is adjusted responsive to liquid phaseoctane number.

6. In a continuous flow hydrocarbon conversion process wherein ahydrocarbon charge stock is passed through a conversion zone atconversion conditions comprising elevated temperature and a firstelevated pressure, and the resulting conversion product effluent isseparated into a vapor phase and into a liquid phase comprising gasolineboiling range hydrocarbon components, said conversion process havingcharge stock preheating means, said conversion zone, a vapor-liquidphase separation zone maintained at a second elevated pressure, meansfor passing charge stock to said preheating means, means for passingcharge stock from said preheating means to said conversion zone, meansfor passing conversion product effluent from said conversion zone tosaid separation zone, and means for supplying heat to said preheatingmeans from an external source, the improved control system for saidconversion process which comprises in combination:

a. operatively associated with said heat supplying means, means to varythe heat input to said preheating means:

b. a hydrocarbon analyzer comprising a stabilized cool flame generatorwith a servo-positioned flame front, continuously receiving a sample ofsaid liquid phase from said separation zone substantially at said secondelevated pressure, and developing an output signal which in turnprovides a measure of sample octane number; and,

. means transmitting said analyzer output signal to said heat inputvarying means whereby the heat input to said preheating means isregulated responsive to octane number of said liquid phase and saidoctane number is thereby maintained at a constant predetermined level.

7. The system of claim 6 wherein said heat input varying means comprisesa flow control loop including a flow controller having an adjustablesetpoint regulating the flow of heating medium through said preheatingmeans, whereby said setpoint is adjusted in response to said analyzeroutput signal.

8. The system of claim 7 further characterized in the provision of meansto sense conversion zone temperature, temperature control meansconnecting with said temperature sensing means with such control meanshaving an adjustable setpoint and developing a temperature outputsignal, and means transmitting said temperature output signal to thesetpoint of said flow controller, with said means (c) transmitting saidanalyzer output signal to said temperature control means setpointwhereby the latter is adjusted responsive to liquid phase octane number.

9. The system of claim 8 wherein said temperature sensing meanscomprises first means sensing the temperature of an inlet section ofsaid conversion zone and second means sensing the temperature of anoutlet section of said conversion zone, whereby said temperature outputsignal provides a measure of temperature difference between said inletand outlet sections.

10. The system of claim 7 further characterized in the provision offirst means to sense a first temperature of said conversion zone, firsttemperature control means connecting with said first temperature sensingmeans with such control means having an adjustable setpoint anddeveloping a first temperature output signal, means transmitting saidfirst temperature output signal to the setpoint of said flow controller,second means to sense a second temperature of an inlet section of saidconversion zone, third means to sense a third temperature of an outletsection of said conversion zone, second temperature control meansconnecting with said second and third temperature sensing means withsuch control means having an adjustable setpoint and developing a secondtemperature output signal which provides a measure of temperaturedifference between said inlet and outlet sections, and meanstransmitting said second temperature output signal to the setpoint ofsaid flrst temperature control means, with said means (c) transmittingsaid analyzer output signal to said second temperature control meanssetpoint whereby the latter is adjusted responsive to liquid phaseoctane number.

11. In a continuous flow hydrocarbon conversion process wherein ahydrocarboncharge stock is passed through a conversion zone atconversion conditions comprising elevated temperature, andthe resultingconversion product effluent is separated into a vapor phase and into aliquid phase comprising gasoline boiling range hydrocarbon components,said conversion process having charge stock preheating means, saidconversion zone, a vapor-liquid phase separation zone, means for passingcharge stock to said preheating means, means for passing charge stockfrom said preheating means to said conversion zone, and means forpassing conversion product effluent from said conversion zone to saidseparation zone, the improved control system for said conversion processwhich comprises in combination:

a. operatively associated with said conversion zone, means to vary theseverity of conversion conditions therein;

b. a hydrocarbon analyzer comprising a stabilized cool flame generatorwith a servo-positioned flame front, continuously receiving a sample ofsaid liquid phase from said separation zone without interveningdepressurization, and developing an output signal which in turn providesa measure of sample octane number; and,

means transmitting said analyzer output signal to said means (a) wherebythe severity of said conversion conditions is regulated responsive tooctane number of said liquid phase and said octane number is therebymaintained at a.constant predetermined level.

12. The system of claim 11 wherein said means (a) varies temperaturewithin said conversion zone.

13. The system of claim 11 wherein said means (a) varies the flow of atleast one reactant within said conversion zone. i

14. The system of claim 11 wherein said conversion process comprises afluidized catalytic cracking process, and said means (a) varies the flowof fluidized catalyst within said conversion zone.

2. The system of claim 1 wherein said heat input varying means comprisesa flow control loop including a flow controller having an adjustablesetpoint regulating the flow of heating medium through said preheatingmeans, whereby said setpoint is adjusted in response to said analyzeroutput signal.
 3. The system of claim 2 further characterized in theprovision of means to sense conversion zone temperature, temperaturecontrol means connecting with said temperature sensing means with suchcontrol means having an adjustable setpoint and developing a temperatureoutput signal, and means transmitting said temperature output signal tothe setpoint of said flow controller, with said means (c) transmittingsaid analyzer output signal to said temperature control means setpointwhereby the latter is adjusted responsive to liquid phase octane number.4. The system of claim 3 wherein said temperature sensing meanscomprises first means sensing the temperature of an inlet sEction ofsaid conversion zone and second means sensing the temperature of anoutlet section of said conversion zone, whereby said temperature outputsignal provides a measure of temperature difference between said inletand outlet sections.
 5. The system of claim 2 further characterized inthe provision of first means to sense a first temperature of saidconversion zone, first temperature control means connecting with saidfirst temperature sensing means with such control means having anadjustable setpoint and developing a first temperature output signal,means transmitting said first temperature output signal to the setpointof said flow controller, second means to sense a second temperature ofan inlet section of said conversion zone, third means to sense a thirdtemperature of an outlet section of said conversion zone, secondtemperature control means connecting with said second and thirdtemperature sensing means with such control means having an adjustablesetpoint and developing a second temperature output signal whichprovides a measure of temperature difference between said inlet andoutlet sections, and means transmitting said second temperature outputsignal to the setpoint of said first temperature control means, withsaid means (c) transmitting said analyzer output signal to said secondtemperature control means setpoint whereby the latter is adjustedresponsive to liquid phase octane number.
 6. In a continuous flowhydrocarbon conversion process wherein a hydrocarbon charge stock ispassed through a conversion zone at conversion conditions comprisingelevated temperature and a first elevated pressure, and the resultingconversion product effluent is separated into a vapor phase and into aliquid phase comprising gasoline boiling range hydrocarbon components,said conversion process having charge stock preheating means, saidconversion zone, a vapor-liquid phase separation zone maintained at asecond elevated pressure, means for passing charge stock to saidpreheating means, means for passing charge stock from said preheatingmeans to said conversion zone, means for passing conversion producteffluent from said conversion zone to said separation zone, and meansfor supplying heat to said preheating means from an external source, theimproved control system for said conversion process which comprises incombination: a. operatively associated with said heat supplying means,means to vary the heat input to said preheating means: b. a hydrocarbonanalyzer comprising a stabilized cool flame generator with aservo-positioned flame front, continuously receiving a sample of saidliquid phase from said separation zone substantially at said secondelevated pressure, and developing an output signal which in turnprovides a measure of sample octane number; and, c. means transmittingsaid analyzer output signal to said heat input varying means whereby theheat input to said preheating means is regulated responsive to octanenumber of said liquid phase and said octane number is thereby maintainedat a constant predetermined level.
 7. The system of claim 6 wherein saidheat input varying means comprises a flow control loop including a flowcontroller having an adjustable setpoint regulating the flow of heatingmedium through said preheating means, whereby said setpoint is adjustedin response to said analyzer output signal.
 8. The system of claim 7further characterized in the provision of means to sense conversion zonetemperature, temperature control means connecting with said temperaturesensing means with such control means having an adjustable setpoint anddeveloping a temperature output signal, and means transmitting saidtemperature output signal to the setpoint of said flow controller, withsaid means (c) transmitting said analyzer output signal to saidtemperature control means setpoint whereby the latter is adjustedresponsive to liquid phase octane number.
 9. The system of claim 8wherein said temperature sensing means comprises first Means sensing thetemperature of an inlet section of said conversion zone and second meanssensing the temperature of an outlet section of said conversion zone,whereby said temperature output signal provides a measure of temperaturedifference between said inlet and outlet sections.
 10. The system ofclaim 7 further characterized in the provision of first means to sense afirst temperature of said conversion zone, first temperature controlmeans connecting with said first temperature sensing means with suchcontrol means having an adjustable setpoint and developing a firsttemperature output signal, means transmitting said first temperatureoutput signal to the setpoint of said flow controller, second means tosense a second temperature of an inlet section of said conversion zone,third means to sense a third temperature of an outlet section of saidconversion zone, second temperature control means connecting with saidsecond and third temperature sensing means with such control meanshaving an adjustable setpoint and developing a second temperature outputsignal which provides a measure of temperature difference between saidinlet and outlet sections, and means transmitting said secondtemperature output signal to the setpoint of said first temperaturecontrol means, with said means (c) transmitting said analyzer outputsignal to said second temperature control means setpoint whereby thelatter is adjusted responsive to liquid phase octane number.
 11. In acontinuous flow hydrocarbon conversion process wherein a hydrocarboncharge stock is passed through a conversion zone at conversionconditions comprising elevated temperature, and the resulting conversionproduct effluent is separated into a vapor phase and into a liquid phasecomprising gasoline boiling range hydrocarbon components, saidconversion process having charge stock preheating means, said conversionzone, a vapor-liquid phase separation zone, means for passing chargestock to said preheating means, means for passing charge stock from saidpreheating means to said conversion zone, and means for passingconversion product effluent from said conversion zone to said separationzone, the improved control system for said conversion process whichcomprises in combination: a. operatively associated with said conversionzone, means to vary the severity of conversion conditions therein; b. ahydrocarbon analyzer comprising a stabilized cool flame generator with aservo-positioned flame front, continuously receiving a sample of saidliquid phase from said separation zone without interveningdepressurization, and developing an output signal which in turn providesa measure of sample octane number; and, c. means transmitting saidanalyzer output signal to said means (a) whereby the severity of saidconversion conditions is regulated responsive to octane number of saidliquid phase and said octane number is thereby maintained at a constantpredetermined level.
 12. The system of claim 11 wherein said means (a)varies temperature within said conversion zone.
 13. The system of claim11 wherein said means (a) varies the flow of at least one reactantwithin said conversion zone.
 14. The system of claim 11 wherein saidconversion process comprises a fluidized catalytic cracking process, andsaid means (a) varies the flow of fluidized catalyst within saidconversion zone.